Eschatos appears 52 times in the NT. Its basic meaning is spatial ('uttermost parts,' Acts 1:8) or temporal ('last days,' Acts 2:17; 2 Timothy 3:1; Hebrews 1:2; 1 Peter 1:5). The theological discipline of 'eschatology' (from eschatos + logos) takes its name from this word — the study of 'last things': death, resurrection, judgment, and the new creation. The NT is profoundly eschatological: Jesus proclaimed the 'kingdom of God' as breaking in with his ministry; his resurrection inaugurated the new age; and his return will consummate it.
The NT uses eschatos in two overlapping senses: 'already' and 'not yet.' Hebrews 1:2 says God has spoken 'in these last days [ep' eschatou tōn hēmerōn]' through his Son — meaning the final epoch of redemptive history has begun with Christ's coming. John says 'it is the last hour' (1 John 2:18). Yet the 'last day' (hē eschatē hēmera) of resurrection and judgment still lies ahead (John 6:39-40, 44, 54; 11:24; 12:48). This tension — living in the 'last days' while awaiting the 'last day' — defines the entire Christian experience. Revelation 1:17; 2:8; 22:13 call Christ the 'First and the Last [ho eschatos]' — the one who encompasses all of history.